This proposal is directed at those surface membrane changes which occur when: (1) cultured mammalian fibroblasts enter a quiescent state within the cell cycle designated GO, and (2) following stimulation of these quiescent cells back into an active growth state using fibroblast growth factor (FGF). Those cell systems to be examined include both normal and transformed or tumorigenic fibroblasts capable of being arrested in GO. Membrane systems to be analyzed during the entrance into, and release from, quiescence will be those serving transport and enzyme functions. The following objectives are to be pursued: (1) a determination of those membrane-function changes occurring in GO which are GO-specific and under coordinate control: (2) when quiescent cells are stimulated back to active growth using FGF, ascertain the time sequence in which these membrane changes occur: (3) determine whether these growth control-related membrane activity shifts are tightly coupled to cell division; (4) compare the response to FGF and serum growth factors of GO-arrested tumor cells to normal cells; and (5) use an in vitro membrane vesicle system to study membrane-function changes involved in growth regulation. The methodology will include induction of the quiescent state by serum growth factor-deprivation. Transport and membrane enzyme activity determinations will be made using radioisotope-labeled substrates, and both intact cell monolayers and cell-derived plasma membrane vesicles. Overall, data will be generated on "pleiotypic" membrane changes and the handling of, and response to, specific growth factors such as FGF by both normal and tumorigenic fibroblasts.